This disclosure relates to thermal-batteries and methods of manufacturing thermal batteries that have a rolled or coiled electrode assembly, otherwise known as a “spiral wound” or “Swiss roll” configuration.
Thermal batteries are primary reserve batteries that utilize an electrolyte that, at ambient temperatures, is a nonconductive solid in a non-activated state. Thus, at ambient temperatures, the electrolyte is solid and inert. When the thermal battery is in use and reaches an operating temperature, the electrolyte becomes molten and is in an activated state. As primary electrical sources, thermal batteries generate a single, continuous energy output once activated. The output interval varies from a few seconds to over an hour depending on the battery type, construction, and design.
In order to achieve an activated state, thermal batteries are provided with a pyrotechnic that is in close proximity to the electrolyte. Once the pyrotechnic is ignited, the thermal reaches a temperature typically within the range of 450° C. to 600° C., wherein the battery reaches an activated state.
Thermal batteries are beneficial in that they provide a large amount of energy relative to their volume. Additionally, as long as they are stored properly (e.g., sealed), thermal batteries may be used years after storage, such as for at least ten or more years, without showing signs of degradation and decay and without the need for additional pre-ignition preparation prior to use. Because of these factors, thermal batteries are useful in many different applications and environments. For example, thermal batteries are used in missile systems such as Joint Direct Attack Munition (JDAM), Stinger, Javelin, BAT smart missiles, as well as other systems such as sonar buoys and ejector seats. Because many of these applications require long periods of storage time before use, thermal batteries are ideal choices for permanent installation as they themselves can experience long periods of non-use.
Typical thermal battery manufacturing processes use pellets, which are then loaded into a cell stack. Specifically, a pressing machine is used to press powders to form anodes, cathodes, electrolytes, and pyrotechnics pellets. The powder material may comprise any number of chemicals or compositions that are known to be useful in thermal batteries. Once the powder material for each element (i.e., the anode, cathode, electrolyte, and pyrotechnic) have been formed into a pellet, the pellets are then stacked in the cell stack in an alternating manner. Conventional thermal batteries and methods of making thermal batteries are disclosed, for example, in U.S. Pat. No. 8,052,764; U.S. Pat. No. 7,871,447; and U.S. Pat. No. 7,926,169, the entire disclosures of which are herein incorporated by reference.
Although conventional thermal batteries are beneficial for the reasons discussed above, the powder pressing step during manufacture limits the size, thickness, and geometry of the cell components, including the cathode and the anode. Additionally, the components tend to be brittle. As a result, conventional thermal batteries are limited to having a planar shape.